Tap water has chemicals called salts dissolved in it. It will have chlorine added to kill bacteria. It might have flouride added to stop tooth decay. It may also have picked up chemicals from the rocks that it flowed over and the pipes that it travelled along. If the tap water is heated in a distillation apparatus and the steam is condensed at the other end, you will collect pure distilled water. Any dissolved gases (such as oxygen) will have been driven out of the water by the boiling. You will have nothing left but H2O, or a compound made up of hydrogen and oxygen.

Bacteriostatic water is not just sterile water, but usually contains an amount of Benzyl Alcohol which slows the multiplication of bacteria (hence it is some times refered to as BA water). It is not really used in this country much (don't know why most freeze dried injectables are prvided with sterile distilled water here). If you are reconstituting for injection, Sterile water should suffice if you then keep the product in the fridge it is used within a week and are sure that the contents of the vial are sterile in the first place!

I don't believe you can buy it in the UK, I just got some from www.cjintnllabsupply.com/ along with some other stuff. They're in the US but it only took 4 days to get here!! Cathy, who runs the place is very cool.